This invention relates generally to gas generant materials such as used to inflate automotive inflatable restraint airbag cushions and, more particularly, to gas generant materials which contain guanylurea nitrate and the use of such gas generant materials.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an xe2x80x9cairbag cushion,xe2x80x9d that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically also include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon system actuation, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an xe2x80x9cinflator.xe2x80x9d
Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as relating to the safe and effective handling, supply and disposal of such gas generant materials.
In view thereof, significant efforts have been directed to minimizing or avoiding the use of sodium azide in automotive airbag inflators. Through such efforts, various combinations of non-azide fuels and oxidizers have been proposed for use in gas generant compositions. These non-azide fuels are generally desirably less toxic to make and use, as compared to sodium azide, and may therefore be easier to dispose of and thus, at least in part, found more acceptable by the general public. Further, non-azide fuels composed of carbon, hydrogen, nitrogen and oxygen atoms typically yield all gaseous products upon combustion. As will be appreciated by those skilled in the art, fuels with high nitrogen and hydrogen contents and a low carbon content are generally attractive for use in such inflatable restraint applications due to their relatively high gas outputs (such as measured in terms of moles of gas produced per 100 grams of gas generant material).
In addition to low toxicity and high gas outputs, fuel components for use in gas generant materials desirably are relatively inexpensive, thermally stable (i.e., desirably decompose only at temperatures greater than about 160xc2x0 C.), and have a low affinity for moisture.
Oxidizers known in the art and commonly employed in such gas generant compositions include transition metal-containing water-compatible oxidizers such as transition metal oxides, transition metal peroxides and transition metal-containing salts of oxygen-bearing anions, such as including basic nitrates, for example. Unfortunately, transition metal-containing oxidizers may undesirably react with other composition materials to form metallic derivatives of a highly explosive nature and which are not generally suited for use in an automotive inflatable restraint system or a gas generating device used in such a safety system. Thus, when including transition metal-containing water-compatible oxidizers in such formulations care is required to ensure that the formulation does not also include a material which may undesirably react therewith to form such explosive metallic derivatives.
U.S. Pat. No. 6,024,812 discloses propellant formulations which include nitroaminoguanidine as a main component, a secondary fuel or explosive ingredient such as dicyandiamidine nitrate (also known as xe2x80x9cguanylurea nitratexe2x80x9d) and an oxidizing agent. This patent discloses that oxidizing agents useful in the propellant formulation thereof include nitrates of alkali and alkaline earth elements, perchlorates of alkali and alkaline earth elements, ammonium nitrate, ammonium perchlorate or mixtures of these compounds.
Those skilled in the art will appreciate that nitroaminoguanidine exists in a form which has acid characteristics and can form metallic derivatives of a highly explosive nature. Thus, oxidizers which contain a transition metal are incompatible with nitroaminoguanidine in known automotive inflatable restraint system gas generation applications.
In typical gas generant compositions, the capability for the composition, including the oxidizer, to be processed via water-based processing has various practical and commercial benefits. For example, through the use of water-based processing, the components of the compositions can be mixed or otherwise processed with more uniformity such as to desirably result in less compositional variability. Further, as compared to dry mixing of compositional components, water-based processing can produce or result in improved material handling safety. Unfortunately, typical peroxide forms of gas generant oxidizers undergo decomposition when put in contact with water. As a result, gas generant compositions which include peroxide forms of oxidizers are typically processed via dry blending and thus, the advantages of water-based processing cannot be realizable therewith.
Further, those skilled in the art will also appreciate that upon combustion the metallic component of transition metal-containing oxidizers typically ends up as a solid. Thus, the amount of oxidizer included in such gas generant materials can significantly effect the amount of gas resulting upon combustion of the gas generant material. In view thereof, efforts have been directed to reducing or minimizing the amount of oxidizer required in such gas generant formulations. One approach used with at least some success in reducing or minimizing the required amount of oxidizer involves the incorporation of oxygen, in greater relative amounts, in the fuel component of the gas generant composition. Thus, desirable fuels for use in such gas generant compositions may preferably include a relatively high content of oxygen.
In addition to the above-identified desirable properties and characteristics, gas generant materials for use in automotive inflatable restraint applications must be sufficiently reactive such that upon the proper initiation of the reaction thereof, the resulting gas producing or generating reaction occurs sufficiently rapidly such that a corresponding inflatable airbag cushion is properly inflated so as to provide desired impact protection to an associated vehicle occupant. In general, the burn rate for a gas generant composition can be represented by the equation (1), below:
Rb=Bpnxe2x80x83xe2x80x83(1)
where,
Rb=burn rate (linear)
B=constant
P=pressure
n=pressure exponent, where the pressure exponent is the slope of the plot of the log of pressure along the x-axis versus the log of the burn rate along the y-axis
Guanidine nitrate (CH6N4O3) is a non-azide fuel with many of the above-identified desirable fuel properties and which has been widely utilized in the automotive airbag industry. For example, guanidine nitrate is commercially available, relatively low cost, non-toxic, provides excellent gas output due to a high content of nitrogen, hydrogen and oxygen and a low carbon content and has sufficient thermal stability to permit spray dry processing.
Unfortunately, guanidine nitrate suffers from a lower than may be desired burn rate. Thus, there remains a need and a demand for an azide-free gas generant material which may more effectively overcome one or more of the problems or shortcomings described above. In particular, there is a need and a demand for gas generant materials which, while effective in overcoming one or more of the problems or shortcomings identified above, also provides or results in a desirably rapid burn rate as required or desired for particular applications while incorporating or using a transition metal-containing water-compatible oxidizer.
A general object of the invention is to provide improved gas generation and, more particularly, to provide improved gas generant compositions and associated gas generant composition-containing devices and methods of gas generation.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through a gas generating composition which includes or contains guanylurea nitrate and at least one transition metal-containing water-compatible oxidizer present in sufficient relative amount such that, upon combustion reaction initiation of the at least one transition metal-containing water-compatible oxidizer with the guanylurea nitrate, reaction products including a quantity of nitrogen gas are produced.
The prior art generally fails to provide gas generant materials which, while avoiding inclusion or reliance on azide or azide-based materials, also suitably satisfies selected criteria such as relating to manufacture and performance. In particular, the gas generant materials of the prior art and such as used in gas generating devices used in automotive inflatable restraint systems, for example, generally fail to provide or result in desirably high burn rates while also satisfying, as effectively as desired, criteria relating to manufacture or performance such as, for example, including:
a) avoidance of inclusion or reliance on azide or azide-based materials;
b) cost;
c) safety;
d) gas output;
e) thermal stability;
f) effluent toxicity; and
g) ease of manufacture or production via water-based processing.
The invention further comprehends a method of generating gas involving reacting a gas generant composition which contains guanylurea nitrate and at least one transition metal-containing water-compatible oxidizer present in sufficient relative amount such that, upon combustion reaction initiation of the at least one transition metal-containing water-compatible oxidizer with the guanylurea nitrate, reaction products including a quantity of nitrogen gas are produced.
Also, provided is an improved method of synthesizing guanylurea nitrate wherein dicyandiamide is reacted with nitric acid.
As used herein, references to a specific composition, component or material as a xe2x80x9cfuelxe2x80x9d are to be understood to refer to a chemical which generally lacks sufficient oxygen to burn completely to CO2, H2O and N2.
Correspondingly, references herein to a specific composition, component or material as an xe2x80x9coxidizerxe2x80x9d are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO2, H2O and N2.
Further, references herein to xe2x80x9cwater-compatiblexe2x80x9d oxidizers are to be understood to refer to oxidizers which are generally stable in water and such as will not generally react with water, at normal processing and handling conditions, to form byproducts.